1. Field of the Invention
The present invention relates to an air-to-fuel ratio control system for internal combustion engines, and more particularly the invention relates to such an air-to-fuel ratio control system adapted to electrically control the air-to-fuel ratio of the mixture supplied to the engine in accordance with the driving conditions including the vehicle speed.
2. Description of the Prior Art
In the past, internal combustion engines, especially those used on automobiles and the like have generally employed carburetors and so designed that the mixing ratio or the air-to-fuel ratio of air and fuel mixed in the carburetor is mainly controlled in accordance with only such operating parameters of the engine, e.g., the throttle opening degree and intake air amount. However, in view of the increasing requirements for exhaust emission control and fuel consumption economy in recent years, a great veriety of carburetor air-to-fuel ratio control characteristics have been required, and moreover greater accuracy for air-to-fuel ratio control has been required depending on the automobile driving conditions.
On the other hand, the essential driving requirements of the driver of an automobile carrying an internal combustion engine at least include that the driver can drive the vehicle at any desired speed, and that improved drivability, e.g., improved acceleration performance is ensured. It is evident that these essential requirements of the drivers are all related to the speed of the vehicles. Thus, in view of the fact that the vehicle speed is related with the above-mentioned social needs, i.e., the exhaust emission control and fuel consumption economy, it will be seen that a vehicle speed parameter must be taken into account in controlling the air-fuel ratio of the mixtures. However, the known air-to-fuel ratio control systems for internal combustion engines have not attached great importance to the vehicle speed.